Long Island Nice Tea

A Top-Five Hottest Year Despite Relief from Major Storm Systems

Author

Adam Kemberling

Published

January 4, 2024

The Importance of the Long Island Sound Region

For analyses like these that characterize environmental conditions for a particular area—in this case, the Long Island Sound—it is important to be clear about the spatial extent that defines the region of study; different domain boundaries could produce different results. The spatial area we use to define the “Long Island Sound” is displayed in Figure 1, and has remained consistent throughout our seasonal and annual warming updates.

An overhead view of the Long Island Sound region. Landmasses and political boundaries for the United States and Canada are displayed. A blue dotted line outlining a box with a transparent blue fill is shown to demark where satellite data for the analysis has been used. — Figure 1: Spatial domain used for Long Island Sound SST analyses. Dotted line denotes region of study for this analysis. Depth contours are colored at 100m intervals to a maximum of 600m, deeper blues indicate deeper water depths.

Highlights from Another Remarkably Warm Year

Over the past decade, scientists at the Gulf of Maine Research Institute have led a body of research that highlights the rapid pace of warming in the Long Island Sound. To keep you informed, we share seasonal and annual updates about conditions in the Long Island Sound.

With an annual average sea surface temperature (SST) of 56.48°F — more than 1.99°F above normal — the Long Island Sound experienced its 5th warmest year on record in 2023. This year fell short of the previous warmest year on record — 2021 — 1.12°F, but was record-breaking in a number of regards.
The first four months this year average monthly SST was within the top 3 warmest among all years on record. With February, March, and April all the warmest on record.
The most extreme temperatures in 2023 occurred in February and March, each setting new records for highest monthly average SST in the Long Island Sound.
The “coolest” monthly average temperature anomalies for 2023 occurred during September, November, and December. Each of last five months this year had SSTs below the top ten warmest.
SSTs in 2023 were consistent with the long-term trend of increasingly warm conditions driven primarily by anthropogenic climate change.

2023 Sea Surface Temperature in the Long Island Sound

Comparing Annual SST to Historical Conditions

When we compare the annual average SST in the Long Island Sound for 2023 (56.48°F) to other years, we can see it narrowly beat out 2012 as the second warmest year on record. When we look at the deviation from the long-term average SST (i.e., the annual SST anomaly), the last decade stands out for its exceptional warmth (Figure 3). 2023 extends a pattern that began in 2010 of sustained above-average temperatures. With the exception of 2019 (ranked 13th), every one of the last ten years remains in the top 10 warmest years on record.

Annual Ranks

Figure 3: A ranking of the top 10 annual SST values [bars] and those years’ respective SST anomalies [x-axis].

Monthly Rankings

?(caption)

Month	Rank (1982-2023)	Observed Temperature	Climatological Average	Temperature Anomaly
Table 1. Monthly Average Sea Surface Temperatures - 2023
January	10	41.1°F (5.1°C)	39.8°F (4.3°C)	1.4°F (0.8°C)
February	3	40.2°F (4.5°C)	36.5°F (2.5°C)	3.7°F (2.0°C)
March	3	41.1°F (5.1°C)	38.0°F (3.4°C)	3.1°F (1.7°C)
April	3	47.3°F (8.5°C)	44.2°F (6.8°C)	3.1°F (1.7°C)
May	4	56.3°F (13.5°C)	53.2°F (11.8°C)	3.2°F (1.8°C)
June	13	63.9°F (17.7°C)	62.9°F (17.2°C)	1.0°F (0.6°C)
July	2	74.0°F (23.3°C)	70.3°F (21.3°C)	3.7°F (2.0°C)
August	13	73.1°F (22.8°C)	72.3°F (22.4°C)	0.8°F (0.4°C)
September	7	72.0°F (22.2°C)	70.0°F (21.1°C)	1.9°F (1.1°C)
October	12	64.5°F (18.0°C)	63.8°F (17.6°C)	0.7°F (0.4°C)
November	9	55.8°F (13.2°C)	55.0°F (12.8°C)	0.8°F (0.5°C)
December	14	47.2°F (8.5°C)	46.6°F (8.1°C)	0.6°F (0.3°C)
Data Source: NOAA OISSTv2 Daily Sea Surface Temperature Data.
Climatological Reference Period: 1991-2020.

Annual Trends

Since the early 1980s, the rate of warming in the Long Island Sound 0.91°F / Decade has been more than triple that of the world’s oceans (0.29°F / Decade Figure 4). The precise causes of the pronounced jump in annual average SSTs in the region from 2009 to 2012 remains an area of active research, but the sustained warm conditions suggest a regime shift in the influence of major ocean currents (i.e., Gulf Stream vs Labrador Current) in the Long Island Sound. While a long-term increase in SSTs is expected as a result of human-caused climate change, we also expect each year to be influenced by large-scale patterns of natural variability, particularly on sub-global (i.e., regional) scales. SST conditions in the Long Island Sound for 2023 retain the region’s distinction as being one of the fastest warming ocean regions on the planet; including the 2023 data shows that the Long Island Sound is warming faster than 97% of the world’s ocean surface.

Figure 4: A timeseries of annual average sea surface temperature anomalies for the Long Island Sound (solid black line) from 1982 through 2023, illustrating that 2023 was the 2nd warmest year on record. Long-term trendlines for the Long Island Sound (blue) and the entire globe (green) show how much more quickly the Long Island Sound is warming compared to the rest of the world.

Quarterly Trends

Zooming in to sub-annual timescales reveals some interesting patterns: the observed rate of warming in the Long Island Sound varies throughout the year. Comparisons across the four quarters of the year (Figure 5) reveal that the Long Island Sound is warming fastest during July-September (~4x the global ocean average)—almost twice the rate seen during January-June (~3x the global ocean average).

Figure 5: Four timeseries panels of the annual averages for 3-month periods (solid black lines) for the Long Island Sound. Decadal trends are overlaid to compare decadal trends in the Long Island Sound (blue) and the entire globe (green). Rates are much faster in the Long Island Sound across all periods, with the smallest difference in rates during January-March.

Daily Sea Surface Temperatures

The annual cycle of SST in the Long Island Sound exhibits a pattern common to regions in the Northern Hemisphere, with the lowest temperatures observed in March and the highest values observed in August (Figure 6). Daily SST anomalies in 2023 never fell below +-1.73 °F compared to the long-term (1991-2020) average and reached as high as high as 5 °F above the long-term average.

The largest temperature anomalies were observed during November, which also turned out to be the warmest November on record (as highlighted in our Fall 2022 update). Figure 6 also illustrates that, in 2023, 353 days experienced SST anomalies that exceeded the threshold for being considered marine heatwaves, or MHW (more on MHWs below, including Figure 7)

MHW Temps

A marine heatwave (MHW) is defined as a period when there are five or more consecutive days when the observed SST is greater than the 90th percentile of the long-term average for that day. Gaps of 2 days or less in this threshold do not constitute a break in the MHW event. Figure 6 illustrates that the Long Island Sound met the criteria for experiencing a MHW for 55 days in 2023 (or 97% of the year). Superimposing MHW status (black line) over the full timeseries of daily SST anomalies (blue/white/red shading) (Figure 6) reveals that the frequency, duration, and intensity of MHWs has increased in the past decade.

A line chart shows the average sea surface temperature for each day of the year, and overlaid against it are notably smoother black lines representing the long-term mean, 10th percentile, and 90th percentile temperatures for those same days of the year. The area between the mean and the observed temperature is filled in with a solid color to indicate whether that day meets marine heatwave criteris. The observed temperatures for 2022 are above the 90th percentile for nearly the entire year, with the exception of two periods less than a week long in June and October. — Figure 6: A timeseries of marine heatwave (MHW) conditions in the Long Island Sound extending from January 1 through December 301 2022. Black lines representing the long-term (i.e., 1991 – 2020) average SST, the 10th percentile (i.e., cold spell threshold), and 90th percentile (i.e., heatwave threshold) for a given day in the Long Island Sound are labeled to indicate climatological reference points. A solid line (red for marine heatwave or blue for a non-heatwave day) indicate the observed SST for each day; red and blue shading illustrates whether each day is considered part of a MHW event.

MHW Anomalies

MHW Heatmap

In a world without human-caused climate change, we would expect, positive (warm) and negative (cool) SST anomalies to more or less balance out over the span of several years, as various patterns of natural climate variability alternate having a dominant influence on Earth’s climate (e.g., La Niña vs El Niño). What is being observed in the Long Island Sound (and elsewhere around the world), however, is a loss of that balance: larger fractions of recent years are experiencing above average temperatures and cold spells are becoming vanishingly rare.

A figure displays the temperatures for each day of year as a colored stripe, organized with a row for each day such that the day of year aligns vertically. The lower two-thirds has a roughly equal balance between colors for warm (red) and cold (blue) temperature anomalies. The top third of the image is almost completely red as temperature anomalies rarely fall below the long-term average. Black dots are overlaid onto days that meet the criteria for a heatwave, they are rare in the lower section and common in the red section. — Figure 7: Heat map of daily SST anomalies from the beginning of 1982 through the end of 2022. Not only do more large warm anomalies (darker reds) appear more frequently in recent years, but the frequency and duration of marine heatwave events (black lines) in the Long Island Sound has become more pronounced in the past decade.

Record Temp Bars

Daily SST values in 2023 were some of the highest ever recorded in the Long Island Sound. Record high SSTs were set for more than half of all days during the months of February, March, & April. February saw the most new records, with 86% of days setting new daily record highs.

Figure 8: An illustration of the percentage of days during each month in 2022 when a record-high temperature was observed in the Long Island Sound (e.g., 80% — 24 days — of November were new record-setting high temperatures).

SST Map

In addition to the sub-annual (or temporal) variation, there can also be significant spatial variability in annually-averaged SST patterns. The Long Island Sound illustrated this fact, with the region southeast of Georges Bank exhibiting the highest annual average SST anomalies (Figure 9). This area is more susceptible than other areas in the region of study to large-scale variability in major oceanic currents, such as the relative influence of the Gulf Stream versus the Labrador Current.

Figure 9: Map of annual average sea surface temperature anomalies in 2021. The box outlined by the black dashed line denotes the region of study for the analysis presented throughout this report.

Quarterly Map

Looking at these spatial patterns across the annual quarters of 2023 (Figure 10) shows not only the large spatial variability in SST conditions, but also how that spatial variability can, itself, vary significantly over the course of the year. While the open ocean beyond Georges Bank exhibits significant spatial and temporal variability, Figure 10 also illustrates that the Long Island Sound experiences more consistent SST conditions spatially and temporally (i.e., the entire region is anomalously warm throughout the year and the warmest areas tend to be those that are most heavily influenced by inflow from the Northeast Channel—the deep valley south of Nova Scotia and just off the northeast tip of Georges Bank).

Figure 10: Maps of the 3-month averages in sea surface temperature anomalies in 2023.

A Note on Data Sources

The figures in this report are created using remotely-sensed satellite data as part of publicly funded research efforts. Satellite SST data was obtained from NOAA’s National Center for Environmental Information (NCEI), with all maps and figures displaying NOAA’s Optimum Interpolation Sea Surface Temperature Data.

NOAA High Resolution SST data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/data/gridded/data.noaa.oisst.v2.highres.html.

A work by Adam A. Kemberling

Akemberling@gmri.org